There is nothing better if you want to understand the actions and movements in war then looking at a map. Hence I have a shelve full of historic and militairy atlasses depicting wars, campaigns and battles. These days however, there are numerous animated maps to be found online which are quite convenient. They of course don't have the 'depth' of these -quite bussy- maps in an atlas but the animation makes them usefull and very interesting all the same.
For an easy understanding of World War II you can acces a some great maps through the links below.